@codex Can you review this PR? Share both good things and rooms for improvements.

I added theactive_only param to usage methods. Instead of modifying turn_usage table, I kept all usage data intact (for cost accounting) but added SQL JOINs to filter by active messages when needed.

Forasyncio.Lock, I keptthreading.Lock to match base class. Changing it inAdvancedSQLiteSession only will require overriding all base class methods, so theasyncio refactor should be a separate PR that touches both classes.

I ran into a bug in my implementation ofreactivate_from_turn(), which uncovered deeper issues. I replaced the broken soft deletion approach with actual branch-based conversation management.

Key changes:

• Addedbranch_id andbranch_turn_number columns to schema, removedis_active/deactivated_at
• Replaceddeactivate_from_turn()/reactivate_from_turn() withcreate_branch_from_turn() that properly copies conversation history
• Fixed the original bug where reactivating would affect both original and new branches
• Added proper branch switching withswitch_to_branch() andlist_branches()
• Updated unique constraints to includebranch_id so turn numbers can overlap between branches

Now each branch is truly isolated - no more weird cross-branch contamination when doing operations.

I understand this might require some extensive review, so take your time.

@seratch awaiting your review

@habema Thanks for being patient here. I didn't have enough time for intensively reviewing this one today, but I will do tomorrow!